1. Field of the Invention
This invention relates generally to infrared communications systems and, more specifically, to an Improved Infrared Signal Communication System and Method Including Transmission Means Having Automatic Gain Control.
2. Description of Related Art
As technology becomes continually more accessible to the “common man,” the ability to use, store, transfer and otherwise manipulate information has become the focus of most businesses as well as for the individual consumer. Access to the information resources is commonly by some sort of network system, including World Wide Web, “Intranets”, local area networks, wide area networks, as well as corporate databases.
While the conventional method for connecting to one of these information networks has been via cable and wire, as the reliance upon connectivity to information has deepened, the desire to gain such access from mobile or portable devices has strengthened. These portable devices, such as Personal Digital Assistants, hand-held computers, cellular telephones, and even digital cameras are now being connected to each other and to networks via Infrared Data Communications. In fact, it is virtually impossible to purchase a notebook computer today that does not include an Infrared Data Communications assembly resident within it.
One drawback of these portable devices or appliances is their inherent dependency upon portable power sources (i.e. batteries of some sort). As functionality is added to the device, so is demand upon the portable power source, therefore any way of reducing the demand upon the portable power source is extremely desirable. One particular system that can place a significant demand upon the portable power source is the Ir transmission subsystem. FIGS. 1A–1C provide pertinent details about this subsystem. FIGS. 1A, 1B and 1C depict Infrared communications between a pair of conventional Ir-enabled appliances. As shown in FIG. 1A, a first Ir-capable appliance 10 is in Ir-communication with a second Ir-capable appliance 12. Of crucial importance to reliable Ir communications is the requirement that the Ir signal transmissions 14 be strong enough to cross the separation distance 16 between the two appliances 10 and 12 (in addition to any other interferences with transmission and receipt).
FIG. 1B depicts one-half of the communications loop depicted by FIG. 1A. In FIG. 1B, the first appliance 10 is the transmitting appliance 11, and the second appliance 12 is the receiving appliance 13. Under the current IrDA (Infrared Data Association) standards, all Ir signal transmissions 14 must be adequate to cross a separation distance 16 of 1 (one) meter. Jn order to achieve this range consistently, devices have been designed with a constant, default transmit power setting (PTXO) that will insure that the receiving appliance 13 receives a certain minimum receive power (PRCVMIN). As mentioned earlier, PTXO is of a constant, fixed magnitude that will result in a received power equal to PRCVMIN when the separation distance 16 is 1 (one) meter.
While this system design does insure reliable Ir communications at the separation distance 16 specified by the IrDA, it is also very wasteful. Under common usage conditions, once a communications loop has been initialized, the transmitting appliance 11 and receiving appliance 13 are usually placed much closer to one another than one meter for the actual data transfer process. As depicted by FIG. 1C, where the separation distance 16 is 0.5 meter, the Ir transmissions “overshoot” the receiving appliance 13. This is a critical problem for a device class (i.e. portable electronic devices) where power efficiency is of primary importance.
FIG. 2 captures the magnitude of the inefficiency of the prior systems. FIG. 2 is a graph illuminating the effect of Ir transmit range on transmit power requirements. It should be understood that there is an inverse square relationship between the transmit distance and the power required to make such a transmission. Consequently, where all transmissions are made at the default power PTXO, there is significant waste. For example, if PTXO is assumed to be 500 mA (i.e. to reach a distance of one meter), then only approximately 25 mA would be required to reliably reach one-half that distance (i.e. 0.5 meter). This means that the transmissions are 80% overpowered at a 0.5 meter separation distance! What would be beneficial would be an Ir transmission system that adjusts its transmit range (and its PTX) to the minimum level for reliable communications (PTXMIN) “on the fly”, so that such power waste is minimized.
FIG. 3 gives additional enlightenment regarding this problem; it is a graph illuminating the effect of transmission distance 16 on received signal strength. It can be seen that at one meter, the magnitude of the received power PRCV is at a level sufficient to support reliable communications PRCVMIN. The problem is that as the separation distance goes to zero, the received power PRCV goes up until it virtually equals the default transmit power PTX0. In this example, at close distances the receiver signal overpower 20 (i.e. the difference between PTX and PRCVMIN) is relatively large compared to PRCVMIN (the amplitude which would provide completely reliable communications). What is needed is a system and transmission method that automatically reduces the magnitude of the receiver signal overpower 20 to minimum levels.